Its gross, but hand-pick any japanese beetles and toss them in a bucket of soapy water, then dispose of them. Plant some beans or peas, whatever vine-y plants they seem to like, nearby, but not too close to your garden. These can serve as the sacrificial lamb for a short while. Get some "milky spore" and sprinkle it everywhere. it does not work instantly, but a few bucks worth of milky spore will attack their grubs in the soil and break their cycle, and it lasts 5-10 years, so it's a great investment!